The present invention concerns a system for feeding fuel from a tank to an internal combustion engine.
More specifically, the present invention concerns a system for feeding diesel fuel from a tank to a diesel combustion engine; application to which the following description refers purely by way of example without this implying any loss of generality.
As is known, the systems for feeding diesel fuel to a diesel combustion engine normally include:
a low-pressure pump or pre-feed pump,
a high-pressure piston pump, and
a hydraulic circuit which is provided with a first branch structured to connect the fuel tank to the pre-feed pump, a second branch structured to connect the pre-feed pump to the high-pressure piston pump and a third branch structured to connect the high-pressure piston pump to the internal combustion engine.
More specifically, in the case of diesel internal combustion engines, the third branch of the hydraulic circuit is able to connect the delivery of the high-pressure piston pump to the fuel distribution manifold, commonly known as the “common rail”, which branches off into injectors which are structured to atomise, on command, the diesel fuel inside the various combustion chambers of the internal combustion engine.
Since the pre-feed pump is a constant-flow electric pump, the system for feeding fuel also comprises an electrically operated shutter valve and a mechanical overpressure valve, placed in parallel along the second branch of the hydraulic circuit.
More specifically, the second branch of the hydraulic circuit branches, downstream of the delivery of the prefeed pump, into two separate channels which reach the high-pressure piston pump separately one from the other. The electrically operated shutter valve is positioned along the channel that communicates directly with the high-pressure piston pump intake, while the over-pressure valve is connected along the channel that communicates with the chamber of the high-pressure piston pump that houses the piston movement mechanism.
The shutter valve is able to continuously regulate the flow of diesel fuel that, moment by moment, flows to the intake throat of the high-pressure piston pump and is piloted by an electronic control unit in a manner such that, moment by moment, a quantity of diesel fuel substantially equal to the instantaneous need of the combustion engine is made to flow to the intake mouth of the high-pressure piston pump, while the over-pressure valve stabilizes the pressure of the diesel fuel upstream of the shutter valve, automatically diverting excess diesel fuel to the chamber of the high-pressure piston pump that houses a piston movement mechanism, so that the diesel fuel can lubricate and cool the mechanical members housed therein.
In recent years, the need to make lighter and more compact the part of the fuel feed system destined to be housed in the vehicle's engine compartment, has driven the majors manufacturers of this type of fuel systems to obtain the two channels of the second branch of the hydraulic circuit directly inside the casing of the high-pressure piston pump, together with the seats that house the shutter valve and the over-pressure valve.
Unfortunately, this need has rendered assembly of the high-pressure piston pump much more complicated; with a consequent increase in production costs with respect to diesel fuel feed systems of greater bulk.